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Are Your Genes Screwing Up Your Diet?

A chat with the scientist who thinks "nutrigenomics" is going to be the next big thing in personal nutrition.

Here are a few things we know about coffee: a few cups a day can help guard against prostate cancer. It’s helpful for a morning bowel movement. It’s also where most Americans get the most of their antioxidants. Beyond that, though, what you hear about coffee and whether or not it’s healthy has probably been inconsistent.

Dr. Ahmed El-Sohemy has an explanation for that inconsistency: coffee, like other food and nutrients, reacts differently to different people because of their genetic makeup. A professor and researcher at the University of Toronto, he found that if you examine a gene called CYP1A2, you can tell how quickly a person metabolizes coffee. If you’re a heavy coffee drinker and a slow metabolizer, then you’re also more likely to develop health problems like heart attacks or diabetes.

I first heard about nutrigenomics while reporting a story about a team nutritionist. Proponents argue that it could be the next big thing in nutrition, enabling people to get personalized advice on their diet based on genetic testing (or better yet: enabling people to get personalized dietary advice through genetic testing). Picture this: What if you knew, on a genetic level, that you’re prone to high blood pressure from too much sodium? Or that you actually possess an overactive sweet taste receptor that primes you to go HAM on cake?

To learn more about nutrigenomics and what it means for eating in general, we spoke with El-Sohemy (who’s also the founder and chief scientific officer for Nutrigenomix Inc., a company that provides genetic testing services) about the field in an attempt to assess whether it really is the future.

GQ: So, first of all, do we still know what a healthy diet looks like?
We generally have a good idea of what is a prudent diet, a healthy diet if you will: one low in processed and refined carbohydrates, low in red meat and processed meats, high in vegetables and fresh fruits and whole grains—that’s just kind of general. You can compare that to a diet high in processed food and red meat and there are massive differences in terms of cardiovascular health, mortality, cancer, and everything under the sun. But if you plot each individual who is eating a bad diet versus a good diet, you’re gonna see some overlap, such that there are some people consuming the so-called "good diet" who actually do worse than some people on the so-called "bad diet." We used to call those the outliers.

But now, according to your studies, there’s a chance that those outliers are caused by genetic variation instead of an error in the data. In your opinion, does this kind of screw up all nutritional studies we’ve got?
Pretty much. We really have to go back and revisit every study we’ve ever done and say, “Okay we see there’s an average improvement or an average effect on some health outcome, but how did the individuals respond?” Is there a genetic difference that can explain why someone is a super responder versus someone who’s a modest responder versus someone who responded in the opposite manner? Whether it’s saturated fat, caffeine, vitamin C, gluten—whatever vitamin or dietary factor, there’s at least one gene if not multiple ones that can impact the way we respond.

Critics would say that genetic testing for nutritional advice is over-the-top, especially since we don’t know all of the genetic factors at play. For example, coffee is really chemically complex, and there’s not enough research for how every gene reacts to every chemical component. Aren’t the general healthy eating guidelines enough?
First of all, most people have been tuning that message out because they hear conflicting findings. Something that’s so widely consumed like coffee, we get conflicting messages about that all the time. One day it’s good for us, one day it’s bad. When someone drinks four cups a day, they want to know if they need to cut back. We’re giving recommendations today based on just a group average.

But we now have many studies that have shown that this one gene, CYP1A2, that can immediately stratify the population between this level versus that level. Is it the perfect advice or the final recommendation? No. As we learn more about other factors we can further fine-tune that advice. But we have to eat today, and right now we give nutrition advice right now based on really old science.

And you’ve done research on how people acted after you gave them their genetic info. What did you find out?
People want to know what works best for them. They don’t really care what gene is activated or turned off when they drink coffee, they just want to know if they should be drinking their coffee or if they should limit it.

In a randomized controlled trial, the gold standard for scientific evidence, we gave people advice to limit their sodium intake a certain amount, and they didn’t do it. But when we said, “You have a gene that increases your risk of salt-sensitive hypertension”—just that one extra line of text then the same advice to limit their sodium intake to a certain amount—they did it and maintained it a year later. From a behavioral science standpoint that’s a pretty profound effect.

You’ve done other research that found that variations in two genes together, a glucose transporter and a sweet taste receptor, can be a powerful factor in overeating. But knowing you’re prone to overeating isn’t the same as finding a cure for overeating, right?
When that study was first reported several years ago it was fascinating to read some of the comments by readers. It’s easy for us to say, “Oh that person’s weak, they should just cut out sugar because I can do it no problem.” You don’t have the same metabolic craving and metabolic driver that make them seek out more sweets. I think there’s power in that knowledge.

I know myself, and I have that version of that gene. Around Halloween time when my kids have leftover candy I’m mindful about not bringing more than just a small chocolate bar to the office, because I know in the afternoon when I get that sugar craving, I’m going to polish it off. It’s empowering to know that.